This invention relates to scaffold equipment and more particularly to a pump jack arranged for traveling up and down a pole.
When placing siding on a building or carrying out other types of construction, scaffolding equipment is required. Instead of erecting complex scaffolding apparatus, there has been developed the use of pump jack poles which are braced to a vertical surface and pump jacks are placed on the poles for riding up and down the poles. The pump jacks support a platform on which the workers stand. By means of a pump arm, which is typically manipulated by the foot, the worker can bring the platform up the pole.
Typically, at least two poles are spanned from each other and braced to the vertical side wall of the building. A pump jack is placed on each pole. The pump jack includes a platform support and planks or other types of platform are spanned across the platform supports of the respective pump jacks. The worker stands on the platform and manipulates the jack by means of his foot which is used to pump the jack and thereby raise it stepwise manner up the pole. Various mechanisms are utilized for lowering the pump jack down the pole. For example, a crank can be provided connected to a spiral which is used to wind down the pump jack.
One early form of pump jack is described in U.S. Pat. No. 2,240,682 which described a number of gripers which alternately grip and release the pole. Numerous levers cooperate with the grippers. One of the levers serves as a pump arm and by oscillating the arm, the jack is raised step by step along the pole.
An improved version of the pump jack is shown in FIG. 1 and includes upper and lower shackles which are alternately caused to grip the pole by means of the pumping action of the foot pedal. When the lower shackle grips the pole, the foot pedal steps up the upper shackle. With the upper shackle gripping, the action of the foot pedal steps up the frame with respect to the pole. The pump jack is lowered by releasing the lower shackle and cranking down the helical rod connected to the upper shackle. This prior art device will be explained more fully hereinafter.
One of the most critical aspects of using a pump jack is its amount of safety. Since the worker is held at very high levels by means of the pump jack, it is of extreme importance that the pump jack is operating in a safe as possible way. However, the specific construction of prior art pump jacks have raised concern about their safety and have brought about a need for redesigning aspects of the pump jack.
Additionally, the specific construction of the prior art pump jack has lead to potential damage to the pole as the pump jack rides up and down and continuously grips the pole. The pump jack itself has caused eating away and cutting into the pole which has also raised a need for redesigning of the pump jack.
Most of the prior art poles heretofore utilized have been wood and typically formed of two 2 by 4s which are fastened together by nails to form a single upright pole. More recently, there has become available a pump jack pole formed of an elongated metal pole having a rubberized surface formed on at least one side of the metal pole. Such metal pump jack pole is described in my U.S. Pat. No. 4,382,488. When utilizing the metal pole described, many concepts previously held with regard to the use of pump jacks and pump jack poles have become modified. For example, it appears that the gripping force of the pump jack is essentially applied on one side with the opposing side serving only as a retaining brace. As a result, modifications of the pump jack are needed in order to further accommodate the use of such metal poles and to enhance the capabilities of the pump jack utilized in conjunction with such pump jack poles.